1. Field of the Invention
The present invention relates to a method of completing a well that penetrates a subterranean formation and more particularly to a method for screen placement during proppant packing of formation fractures to prevent premature bridging of the proppant.
2. Description of Related Art
A long-standing dilemma in the petroleum industry is the production of unconsolidated materials, e.g., sand and other fines, from unconsolidated hydrocarbon-bearing formations. Erosion of production equipment, well plugging, and reduced production levels or loss of well production are some of the consequences of this problem if left unaddressed.
Gravel packing is commonly used to reduce the amount of unconsolidated materials produced along with hydrocarbons. Slotted or screened liners are used during gravel packing to prevent the sand and other fines from being transported by produced hydrocarbons into the well bore. Consolidating plastic material may also be used to cement the grains together to provide formation stability while maintaining permeability.
In addition to gravel packing, frac packing includes hydraulic fracturing wherein the unconsolidated formation is fractured and propping material is deposited in the fracture. The two step method of frac packing in its simplest form involves 1) hydraulic fracturing of the formation, i.e., injecting a fracturing fluid down a well at sufficiently high pressure to propagate a fracture into the subterranean formation; and 2) incorporating proppant materials within the fracturing fluid and injecting and depositing the proppant in the fracture(s).
The proppant is commonly mixed with a fluid, such as a liquid or foam, to form a slurry of the proppant which is then introduced through a work string and a crossover tool into the annulus between the well bore and the liner. The slurry is pumped down the annulus to the bottom of the well bore or to a sump packer in the well bore. The bulk of the slurry fluid flows into the subterranean zone through perforations in the wellbore. Proppant is thus deposited in the annulus and against the subterranean zone. Some of the fluid of the slurry can be allowed to flow through the apertures in the liner into the open bottom end of a wash pipe situated within the liner and return to the surface through the crossover tool and the annulus between the work string and the well casing.
Despite the effectiveness of fracture proppant packs, once the screened liner is properly placed, it is often difficult to install a uniform proppant pack in a frac pack operation due to the problem of premature bridging as the proppant laden fluid is being pumped. Premature bridging occurs when the upstream perforations, that is, the perforations first encountered by the proppant laden fluid, fill with proppant from the proppant slurry and form deposits or bridging which impede the flow of the slurry down the annulus. When this occurs, the slurry follows the path of less resistance, which in this case is through the screen. This in turn accelerates the bridging action, as flow of the slurry fluid through the screen deposits proppant on the upper most portion of the screen. While bridging in this manner can occur in a vertical well, the problem is more severe in a deviated well, where proppant transport through the horizontal well bore annulus is more difficult because it is not assisted by gravity.
U.S. Pat. No. 5,062,484 teaches a method of preventing bridging when gravel packing a well in fluid communication with a subterranean formation by sealing the upper apertures of a gravel pack liner against entry of a slurry fluid. This prevents gravel from clogging the apertures or bridging the annulus between the liner and the well bore. An immobile gel provides the sealing function and a breaker, which can be incorporated into the gel, eventually breaks the gel thereby permitting removal of the gel and unblocking the apertures.
It is an object of this invention to provide a method to prevent premature bridging in hydraulic fracture packing operations in a manner which does not impair or slow the proppant placement process.
It is another object of the present invention to provide a method for gravel packing and/or frac packing a subterranean well which results in the formation of a substantially uniform gravel pack over substantially the entire length of the area to be packed.
Another object of the present invention is to provide a method for gravel packing and/or frac packing a subterranean well which is economical, efficient and which is operable in vertical or deviated wells.